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At the Limits of Feasibility

From day one of the computer industry, the latest generations of computers have constantly surpassed themselves with their processing speed. The minute a computer is purchased, a newer and faster one appears on the market. The rapid gain in speed is also referred to as Moore's Law, which states that the number of transistors on a chip will double every two years. And the more transistors it has, the less time a computer needs for processing.

At the same time, the transistors are becoming smaller and smaller and contain fewer and fewer atoms. However, long before chip structures shrink to the dimensions of individual atoms, effects occur that disturb the functional performance of the classic complementary metal oxide semiconductor (CMOS) transistors.

Silicon WaferCopyright: Forschungszentrum Jülich

At Forschungszentrum Jülich, innovative structures and materials are developed in order to provide enough processing capacity for the applications of the future.

One constraint of CMOS transistors is that all their components lie flat on the surface of a semiconductor. Components that are too close together influence each other through leakage currents and interferences and the transistor loses the ability to switch properly.

One solution could involve three-dimensional structures, such as nanometre-sized walls or columns on a silicon surface. The transistor parts could then be arranged such that they shield each other from the interferences. The researchers at Jülich are using electron beam plotters and ion implantation to produce innovative structures like these and are studying them with high-resolution electron and scanning electron microscopes.

Another constraint is the mobility of the electrons in the silicon semiconductor. This material constant stipulates a lower limit for the speed with which transistors can switch, meaning the processing speed of the chip. Here, strained silicon could be the answer. With a patented method developed at Jülich, the crystal lattice of the silicon is mechanically strained and expanded. The electrons can move more quickly, the switching frequency increases and the power uptake drops. This opens the way towards more powerful and efficient transistors.